[1010.2752]
Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope

Authors:

Dan Hooper, Lisa Goodenough

Abstract:

We analyze the first two years of data from the Fermi Gamma Ray Space
Telescope from the direction of the inner 10 degrees around the Galactic Center
with the intention of constraining, or finding evidence of, annihilating dark
matter. We find that the morphology and spectrum of the emission between 1.25
and 10 degrees from the Galactic Center is well described by a the processes of
decaying pions produced in cosmic ray collisions with gas, and the inverse
Compton scattering of cosmic ray electrons in both the disk and bulge of the
Inner Galaxy, along with gamma rays from known points sources in the region.
The observed spectrum and morphology of the emission within approximately 1.25
degrees (~175 parsecs) of the Galactic Center, in contrast, cannot be accounted
for by these processes or known sources. We find that an additional component
of gamma ray emission is clearly present which is highly concentrated around
the Galactic Center, but is not point-like in nature. The observed morphology
of this component is consistent with that predicted from annihilating dark
matter with a cusped (and possibly adiabatically contracted) halo distribution
(density proportional to r^{-1.34 \pm 0.04}). The observed spectrum of this
component, which peaks at energies between 2-4 GeV (in E^2 units), is well fit
by that predicted for a 7.3-9.2 GeV dark matter particle annihilating primarily
to tau leptons with a cross section in the range of 3.3 x 10^(-27) to 1.5 x
10^(-26) cm^3/s, depending on how the dark matter distribution is normalized.
We discuss other possible sources for this component, but argue that they are
unlikely to account for the observed emission.

Possibly not. Though I'm not a Fermi scientist, I work near some. One comment I overheard was that a bubble from multiple supernovae could be a viable alternative.

Also, treating the Fermi point spread function as a Gaussian is apparently a big mistake – the region of interest in this paper is at the limit of Fermi's resolution, from what I understand. (One scientist, to remain unnamed for dignity reasons, suffered a fit of giggles upon hearing about the Gaussian approximation in this paper.) Finally, I got the impression that the Galprop people were somewhat uncomfortable with how their models were used.

Hopefully, the authors and the Fermi folks will have a sit-down soon and hash out any oversimplifications. Nothing like a little competition to bring out the best science!